JS function that inserts a value between each elements of an array

insertBetweenElements.js

function insertBetweenElements(arr, value) {
  // Get first element in array
  var first = arr.shift();
  // if array is empty return array
  if (!first) return arr;
  // insert the value
  return arr.reduce(function(valeurPrecedente, valeurCourante, index, array){
    return valeurPrecedente.concat(value,valeurCourante);
  },(Array.isArray(first) ? first : [first]));
};